Carrier-wave signaling system



July 19,1927. 7 1,636,134

J. W. HORTON CARRIER wm: SIGNALING SYSTEM Filed Jan. e, 1923 5 sheets-sheet 1` /D/ PJ' P2 P4 @WV- J J g .EVT-WJ l I J2 l l J5 1 i e a I sch/ sa; g sac/121 Rec/7l Rr {RBC/2 1 I 1 @mi i I @Til i J4 V J5 vt i v i E L" L l /HV/v/or.- Jose-ph WHO/fof? July 19, 1927.

J. W. HORTON CARRIER WAVE SIGNALING SYSTEM Filed Jan. e,A 192s s shets-sheet 2 Van J .Q T m H TWFIIJ m /h d u 3. m., 7, 4% w .w 6. wvbww mi l 5 om ol W nu wu u M. f n wur 2. A 9 (W11 Y Jul 19 1927. l

y J. w. HoRToN CARRIER WAVE SIGNALING SYSTEM 5 Sheets-Sheet 3 Filed Jan. e, 192:5

Y switching arrangement, these same .devices Patented July 19, 1927.

" UNITED- STATES;

PATENT olrlcr.. g l

JOSEPH W. HORTON, oF BLOOMFIELDfNEW JERSEY, AslsrGNoR 'pro WRsTERNELRC- frRrcooiuraNY, INCORPQRATED, ory NRW YORK, N. sa,v A CORPQRATION oF NEW YORK.

CARRIER-WAVE' SIGNALING` SYSTEM.

Application led January This invention relates to carrier wave 'sig-v well entitled LfCarrifer current telephony and telegraphyf which is published' in the Trans-- actions of the American `Institute of Electrical Engineers Volmne XL, 1921, describing some of those systems. The equipment` of this invention isalso adapted to cooperate with modifications of those systems, especially a modification in` which different carrier frequencies are usedfor transmissions in opposite directions for a given two-way channel as well as for separate channels.

An object of this invention is to provide a simple carrier telephone equipment by means of which both telephone transmission and call signals may be transn'iitted over a carrier transmission line.` AnotherA object is to provide both a cheap and light weight equipment for this purpoze. Still another object is to provide such an equipment which will cooperate with. various types of permanent carrier wave equipment. `And yet another object is the provision of portable carrier wave terminal equipment.

According to the present invention, a circuit arrangement is provided for a cheap, light weight carrier wave telephone channel in which the same electron discharge devices are made to function in a variety of ways. For telephone transmission they are used in one way; for telephone reception, inv a different way; and for call signaling, in still' another manner. By means of a unique perform their severalfunctions with a minimum of supervision on the part' of the-operator. i

The novel features which are, consideredl characteristic of this invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation together with the objects and advantages there- 6, i923. serialA No. 610,975.

of, will best be understood by reference to the followingdescription, taken in connection with the accompanying drawing in which F ig.v 'l shows thepreferred arrangement of' the invention to meet certain requirements; andl Fig. 2, the terminal yswitching arrangement of a carrier current system` with which the arrangement of Fig. l may be used. F ig; Sshows a modified arrangement suitable for a somewhat different purpose.

Fig. 4 is a simplification of the system ofA plifier MDA, and an amplifier-detector AD' are associatedwitln a telephone handset HS, a ringing switch RS, a Vtransfer switch TS, and plugs P1, P2, P3, and P4 in such a way that either telephone modulated carrier current or` call. signals may be either transmitted fromor received at the station shown.` The oscillator O comprises 'an electron discharge device 5 having a cathode 6, a gridl 7, and a plate 8. The grid-cathode circuit lof device 5 is coupled to the plate-cathode circuit by means offtransformer 9 innwell known manner. The frequency of the generated oscillations is determined primarily by the in-v ductance of the gridf circuit winding of transformer 9` and variable condenser l0 connected in shunt therewith. The output circuit of the oscillator O is completed through thek left hand normally open contactv of relay l1 and potentiometer l2'. The modulator-demodulator-amplifier MDA comprises an electron discharge devicev Y13 having a cathode 14, a grid 15 and a-plate 16. When functioning as ademodulator or amplifier, the'input circuit-'comprises a transformer 17 and normallycl'osed rightfhand back contacto-f relay 11; Vhe'n functioning as a` modulator, the input circuit comprises transformer 17, right hand front contact of f relayll, and potentiometer 12. The amplifie'r-dete'ctor AD comprises theelectron dis-V chargedevice 18 havinga cathode 19, a grid 20, and a plate 21. The tilament-cathodes 6, 1e and 19 of devices 5, 13 and 18 respectively are connected in serieswith each other and supplied with heating current from battery through Variable resistances 23 and 2-1. Plate current 'for each ot' devices 5, 13, and 18 is supplied by battery 25 through chole coils 26, 27 and 28 respectively.

The handset HS comprises a transmitter T, a receiver R, and a control switch CS. Direct. current ttor the transmitter T is supplied by battery over a circuit which may be traced Ytrom the ground side oft battery 22, transmitter T., primary winding oll transi'ormer 29, choke coil 230 to the other side ot battery Receiver R isrnornially connected to the output circuit ot amplilieidetector Al) through the normally closed baclr contacts ot relay 31 and transformer 32. The operation ot controlswitch CS closes an energizing circuit for relays 11, 31 and 3 3 for current it'rom battery 22 which circuit may be traced from the ground side oft' battery 22, control switch CS, conductor Se, windings of relays 11, 31 and 33 in parallel, conductor 35, to the other side ot battery 22. The operation ot control switch CS changes the circuits from the normal receiving condition to the transmitting condition.

Conductors 3G are adapted to receive current incoming to the circuit by way ot plugs P1 or l)g depending upon the position ot transfer switch TS. Conductors 37 carry current outgoing from the circuit to either plugs P or l4 likewise depending upon the position ot transiter switch TS, For tele phone and call signal transmission purposes, ringing switch RS is closed in its lower position. For receiving call signals, however, from a distant sat-ion, ringing switch RS s closed `in its upper position in which case, the energizing winding oit relay 38 is connected in series with plate battery 25 in the output circuit of ampliher-detector AD. The circuit `for this relay may be traced trom -the ground side oit battery 25 through baltery 25, winding of relay 38, right hand blade of ringing switch RS in its upper position, plate 21 and filament- 19 ot discharge device 18 back to the ground side ot battery 25. By means ot the middle blade of ringing switch RS in its upper position. a. circuit is completed at one point for call signaling device 39 through battery L10. one or the other closed posit-ions olf' the middle blade of transfer switch TS and Yiront. or back contact ot relay 38. At the lett hand blade ol ringing switch'RS in its upper closed position, battery l11 in series with re4` sistance 4t2 is connected across the input circuit of discharge device 18.

Referring now to Fig. 2, a typical terminal arrangementof a carrier wave signaling system is shown. A carrier transmission line ML adapted for the transmission of both on dinary telephone current and carrier wares is connected to an ordinary telephone line 5U through the low pass filter Ll" and to the 'arrier terminal equipment by means ot the common carrier circuit 51 through high pass lilter HF. The filters LF and lll? are ott the general type described in Campbell Pat ent No. 1,227,113, May 22, 1917, and are used in the manner described with reference to Fig, 15 oit the article by Messrs. Colpitts and Blackwell supra. Connected to 'the carrier circuit 51 are two two-way channels. Channel h i. 1 coniprises a. sending branch Sl?) .h1 and a receiving branch RB Chl. Channel No. 2 comprises` a sending branch SB Ch2 anda receiving branch il?) Chg. Each oi" these branches includes a band tilter, two only oll which are illustrated, name ly, the sending band tilter tfllil ol5 chamiel No. 1 and the receivingl band litter Rill!" oi the same channel. These iilters are oit the general type disclosed in the Campbell ,latent hereinbe'iore mentioned, and the arrangement o't capaeitatiye and inductive elements shown in Fig. 5 may be used. These lilters are adapted to pass a band ot frequencies indiyidnal to the branch with which the lilter is used. Associated with conductors .'12 and 54 is pernumcnt carrier current terniinal apparatus suoli as is described in the Colpitts and Blackwell paper supra. Similar appie ratus is likewise associated with conductors 55% and Two terminal channels only are shown in Fig. 2 but it is understood that additional channels may be associated Vin the same manner.

For use with other apjnn'atus in a manner herein to be described. jacks J 1 i re included in the carrier circuit 51, jacks ,l2 and J4' in the sending branch Si?) Ch1 of channel ilo. 1 and jacks Ji" and J5 in the receivingbranch RB Ch1 ot channel No. 1. Jacks similar to J2 to 'V' inclusive are included in the sending` and receiving branches ot channel No.

One method oit signaling over the carrier transmission line ML by means ot the carrier terminal equipment ot Fig. 1 located at each end of the line will now be described Assume that this is the only carrier trans mission channel to be operated at a given time over the line ML; therefore. there will be no need for selective separation ot several carrier currents at the terminal stations. Terminal equipment of F 1 will be con` nected to the carrier line ML by the insertion of plugs PJ in jacks J1. Transfer switch TS will be thrown to its lett hand closed position as shown in Fig. 1. The insertion ot plugs P1 in jacks J1 disconnects the carrier terminal equipment below jacks J1 from the carrier circuit 51 at the open contacts of jacks J1 (normally closed).

ln order to transmit a call signal from one station to the other, the control switch Cf? at the calling station is actuated.. This,

liti

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`of plugs P1 in jacks Jli pleted at the left-V liand closed frontcontact (normally open) ot' relay 11 whereupon os- Uri cillations will be generated. these will be supplied to the i-nput circuit of modulator-4 denioduilator-amplifier MDA by means of potention'ieter 12 and right hand closed front contact '(norn'ially open) of relay 11.

The modulator-demodulator-amplilicr MDA acting as an an'ipli'lier will impress the amplified oscillations upon the input circuit of amplifier-'detector AD. VThe ringing switch RS,-being in its lower closed position, connects the resist-ance 42 through its left hand blade directly across this input circuit and thereby provides a resistance coupling betwccn devices 13 and 1S.- The amplified oscillations from amplifier-detector AD are transmitted through transformer 32, front closed contacts (normally open) of relay 31, conductors e3, conductors 36, Vplugs P1, jacks J1,`ca-rrier circuit 51, high pass filter HF to the carrier transmission line ML. No current will flowin conductors 37 because, under the assumedcircuit conditions, plugs P2 are unconnected. Under other conditions, hereinafter to-be described, such as in n'iultiplex operation, these plugs are required. 'l'he transmitter T is connected to the input circuit of modulator-demodulatoramplifier MDA through transformer 29, potentiometer stil, closed front contacts (normally open) of relay 33 andtransformer 17. No use is made of this connection, however,

for the call signal transmitting purposesk now being` described. Thus carrier current is transmitted' over the carrier line ML as lpng as thccontrol switch CS is actuated.

The reception of call signals at the distant station will now be described in connection with the circuits of Figs. 1V and 2 connected as just described by the insertion The circuit arrangement will be identical with that just described, except that the ringing switch RS Awill be closed in its upper position and the cont-rol switch GS will not be actuated. Under these conditions, relays 11, 31, and 33 will be deenergized and the oscillator O will be quiescent due to theV fact that its output circuit is open at the left hand contact of relay 11. The potentiometer 12 is disconnected from the input circuit of modulator-demodulator-amplilier NMDAk at the right hand front contact (now open) of relay 11 and a shorten-cuit is .substituted therefor at the 'back contactl (nowv closed) of relay 11n Current incoming from `the carrier line' ML flows through highv 'pass' filter' HF, carrier` circ'uitLjacks J1,'plugs" P1, left hand closed cont-act of transfer switch YTS, 'conductors 36, back contacts of Arelay 33, transformer 17 to the input circui-tof deviceA 13. This device13 acting as an amplifier impresses current upon the amplifier-detector AD which acts as a` dc- `tector due to the negative polarizing battery 41 limpressed upon the grid 20 by way of theleit hand `blade ofv ringing switch RS in its upper closed position. "lhe device 18 causes the encrgization of relay 3S which v in turncloses theenergizing circuit of calling device 39 at' the front closed contact (normally open) of relay 38. The operator at this station will respond by throwing his 'ringing switch RS to its lower closed position, closing his control switch CS and speaking into his transmitter lli The `calling operator'will listen at his receiver at intervals during thev ringing operation and will therefore, hear vthe calledop'erator when he answers.

The course of a telephone message will ".z

now be followed; Atthe sending end, control switch CSI will be actuated. The operator will talk into his transmitter T which will' cause voice frequency current to flow through.' transformerA 29, potentiometer fiat, closed front contacts (normally open) of relayv 33, transformer 17 to the input circuit of modulator-demodulator-amplifier VMDA through theright hand front contact (normally open) of relay 11 and potentiometer 12. The device 13 functioning as a modulator will transmit carrier waves, modulated in accordance with voice frequency waves over the same circuit as traced for callsignal carrier waves to the carrier line These waves incoming fioin the carrier line ML at the receiving stationv will be iinpressed upon the modulator-demodulatoramplilier MDA in'the same manner as were the calling carrier waves previously doscribed` and will be demodulated by device 13 acting as a` demodulator. For receiving speech, switch RS will be closed in its lowermost position. The voice frequency compenent in the output circuit of the modulatordemodulator-amplilier MDA will be amplified in the amplifier-detector AD acting` as an` amplilier and impress'edfupon the receiver R through the transformer 32 and the closed baclrcontacts of ,relay 31. For transmission in the opposite direction. the

position of the control switches CS at theV two Astations will be reversed. The di rect-ion of flow of -bo'th the call sig? nal carrier waves" and the voice modulated carrier wavesjV under the circuit conditions just described are shown by the dotted arrows.' .Y i

Another method will now be described.

For this purpose assume that itis desiredk to communicate over one" channel lof a 'mul- Y n tiple'X carrier wave'signaling'systeni by employing frequencies which yare not normally employed in that system. Terminal equip- Siu.

ment corresponding to Fig. i will be used at cach end ot the carrier line ML. It the same carrier frequencies are used tor transmission in both directions7 band filter such as shoun in Fig. 5 may be used. The plugs Pl Vwould be uf'ithdrawn from jacks J1 and inserted instead in jacks il of iilter BF. The other terminals ot tilter BF Would be connected to the carrier circuit 5l by means ot the patching cord PC ot Fig. 6. Plugs P would be inierted in jacks J7 and plugs lm in jacks J2. lhe frequency ot oscillator O Would be so. adjusted that the carrier ware 'Frequency with its modulated side baud frequencies would lie within the range or band lilter BF or lookingat the. matter in anotlfer Way, the constants ol band itilter BF would be so chosen as to transmit the carrier trequency ot oscillator O together with its roice modulated side band or bands. The operation of the call signal and Voice transmissions would be identical with that previously described.

ssun'iing still another condition, it might ce desirable to employ one of the channels such as channel l ot Fig. 2 for transmission by means of the arrangement ot Fig. 1. in this assumed case, the sending band iilter SBF and the receiving band filter BBF ot the terminal equipment ot Fig. 2 would be employed to ei'i'ect frequency s lection. in this case, plugs P1 would bc inserted in jacks and plugs l?g in jacks in this case, it is assumed that different, frequencies would be used 'tor transmissions in opposite directions and the sending band tilter SBF at one station nould pass the same range oit frequencies as the receiving band tilter HBF at the other station; while the receiving band tilter Ril-3F at the first station would pass a ditierent range ot frequencies, although the same range as would be passed by the sending band lilter at the other station. The Jfrt-rquencies ol' the generated cai'- ricr oscillations would be adjusted to correspond to the ranges ot frequencies to be employed.

The path of the carrier waves under these circuit conoitions, Will now be traced 'trom the sending to the receiving station. The control switch (lfd at the sending station will be actuated.r Carrier Waves it'rom the oscillator` O will traverse the modulatordemodulator-amplitier lie-TDA., the ampliiierdetector AD? transformer closed 'front contacts (normally open) of relay ai, conductors 37, lett hand closed contacts or the right hand pair ot blades ot transier sr-:itch TS. plugs P2. jacks J4, sending` band tilter SBF, normally closed contacts oit jacks J2. the end sections ot the other channel band lilters, normally closed contacts of jacks J1, carrier circuit 5i, high pass tilter HF to the carrier transmission line ML.

Carrier Waves incoming 'from tie carrier line ML willA tray much the same circuit entering receiving branch RB Chl through receiving band filter HBF, jacks d, plugs F1, lett hand blades of transfer switch TS in the leithand vclosed position, closed back contacts ot relay 33, transformer 17, to the input circuit ot modulator-demodulatoramplilier MDA. From that point on, the circuit for call signaling or voice transmission will be the same as has been liereinbefore described.

lu some cases, it may be found desirable to carry on carrier wave signaling over one carrier transmission line ML as just described and at the same time to carry on carrier 'Wave signaling over a second carrier transmission line similar to lt/IL in cooperation with a permanently installed carrier terminal station at the distant end of the second line. The arrangement oit the permanently installed distant station may be the same as that shown in Fig. 4t2 of the tlolpitts and Blackwell article hereinbefore imnitioned. For comn'iunication with such permanently installed terminal station terminal plugs P Would be inserted in jacks J and plifgs l in jacks J4. 'l` he band ilters SBF and HBF ot Fig. 2 Would be designed to cooperate with the corresponding band Viilters ci the pern'ianently installed equipment at the distant stat-ion. The trans'ter switch TS would be closed in its right hand position.

is described in the Golpitts and lillacluvell article referred to hereinbc'lore, call signalingl is eli'ected by interriqiting the llow ot carrier waves which are normally present on the carrier transmission line in that system. The call signaling equipment otf Fig. 1 is adapted to cooperate with such a system with the transfer switch TS in its right hand closed position. lVith carrier waves c r ntinuously incoming, and ringing switch RS in its upper closed position, rela-y 35% would be coi'itinuously energized. The en- 1].. ergizing circuit ot calling device 39 would thus be normally kept open at the bacl; contact ot relay 38. iin interruption oli the tlow ol carrier waves lor call signaling would allow the armature of relay 38 to fall 11| back and the callingl device 3S) would be actuated over a circuit which may be traced loo ' trom battery 40, right hand closed position ot the center blade ot' transfer switch TS, closed back contact; ol' relay 38, center blade 12a ot ringing switch RS in itsI upper closed position and calling device 39 back to the other side of battery 40.

Voice transmission would be the same as that preriously described in connection with 125 theV circuit arrange-ment lirst assumed.

I It is thus seen that the circuit arrangement ot F ig. l permits of a Variety ot functions eine' performed by' that eouipinent, Due to v the :tact that the saine devices are used for a lao lit) variety of purposes, this arrangement per'-, mits of the use ofcomparativelycheap and light weight equipment. vThis equipment hasibee'n tried out in practice and found to Werl; satisfactorily. Y

Ansomewhat ditl'ereut type of equipment for accomplishing somenf'hat'the same purpose is slniwn in Fig. 8. lh'isarrangement is intended for use in connection With carrierasystenis employing different frequencies 'for transmissions in opposite directionsand` in which the"unmodulated Waves of carrierY frequency are suppressed at the sending station, only the vmodulated components of thev carrier Waves lbeing transmitted to the disi tant station.l The arrangen'ient of Fig. 3 can also be used With the terminal arrangement of FigQ in the several ivays discussed' in connection with the arrangement of Figi l.

A balanced arrangement of' electron discharge devices similar to that of Scriven Pat-` ent No. 1,396,786, November'l, 1921, is em:- ployed in the arrangement of Fig; 3. TWO electron discharge devices 75 and 76'have` their filaments directly connected together' and heated by current from battery 77. The 1 plate circuits are supplied in parallel with current from battery 7 8 through choke coils 79 andSO. Alternating current energy from the output circuit is fed back to the input circuit through conductors 81 or 82 by means oit transformer 83 or S4 depending upon whether the circuit is arranged for reception `or transmission by meansof control switch CS; Any one or severalcondensers4 may be connectedin parallel with the plate circuit winding of transfori'ners 83 or Selby means of switches 85 and 86 for determining ie frequency `of the oscillations tobe` gen- @ratedy by devices 75 and 76 with their associated circuits.` As clearly explained in the Scriven patent hereinbefore noted," the' unmodulated generated oscillations are not 55 transmitter Tgloiving through loyvpas filterv impressed upon the output conductors 87 by means of transformer 88.

It' 1t desired to use the-arrangement of Fig. 3 Withthe carrier.transmission line ML of Fig. 2 and only a single carrier sigl'i'aling` channel desired, plugs Ptof Fig.`3 may be inserted in jacks l1 of Fig. 2. In order to en'iploytlie` arrangement of Fig.' 3' for sendingpurposes, the control switch CS would beactuated.- An energizing circuit for relays 89 and 90 would thereupon befcom'i pleted` the circuit "of: which `may be' traced from battery `91, ivindingof'relay 89, coni ductor' 92, winding of relay 90;"eonducto1`f 93',V control switch' CS back` to the 'otherside tof battery 91. The-energizing of relay 89 would cause energyy from the out-put circuits of devices and 76 to be' fed backto the input circuits oftliese devices through transforinfer 84 over the closedfront contact of' relay 89. Speech frequency currents from LPT and input transformer 94, Would be' differentially impressedupon the input circuit of devices 75 and 76, by means of which' devices, the speech'mod'ulated component of the carrier frequency wouldj be impressed upon conductors 87 by means fof output transformer 88. f This current would flow by Way of plugs P7 andfiacksJl to the carrier transmission line' ML. `The low pass filter Llflt' preventsthis modulated component of the carrier frequency from being impressedV upony the receiver R' and uselessly vv'astedj At th'e distant station, an arrangement identical' with Fig. 3v` would be connected' to the carrier transmission line ML and for reception purposes, the control switch CS Would'be in its openposition" as shown. Under these conditions, speechv modulated` energy'in'coming from the carrie-r transmission-line ML byway of jacksJ'l and plugsV Pt would be impressed upon' conductors' 95 attherclosed :back contacts'of relay 90. It

will be' noted tl'iatboth relays `90 and 89 areI deenergized' for reception purposes: The speech modulatedlenergyin conductors95 isl difierentially impressed upon devices 75 andv 7 6' by nieansof transformer '94andthe demodulate'tlvoice frequencies are impressed upon conductorsv 87 b y means of transformer 8S. This current passes through low pass filter LPR and actuates the receiver dit.rv

These currents are prevented"from vpassing into the .carrier transmission IlineV ML by means of high pass filter'HF of F ig; 2. The speechl `modulated energy infconc'luctor's` 95 isprcvented fron'ibeing Wasted in the trans'- mitterT by inea-ns ofthelow' passlilte'rYK LPT.

For: transmission -in` a "given'v'directiong it is understoodof 'course' that the frequencies em'ployedby'both the transmitting and receiving stations are identical. Different fre` queneiesmay be employed for transmissions inv opposite directions'on tlie'same channel as well as' in the same or opposite directions on' different channelsl v lf it is desired-to Vuse the'arrai'igement of Fig. 3 ,at the same' time that other channels of'Fig; 2 Y beenxployed. Plugs Pf andfP6 correspond respectively to plii's P" and P2 or P3 and P of Fig. 1 and for telephone transmission may. be used to perform the saine functions as the corresponding plugs'of F 1g.` 1.

The arrangement of'Figjlis `z r`simpli'- 'cation'otthat ofi Fig.' 1, only asingle plug Psbei,ng provided. By means of plug" vP,-much`the same'functions are performed by the arrangement of Fig. las were per'- "ffoim'edby the arralngenientofiFig.L 1 as hereinbefore'described when plug P1 is used` alone.

arebeing used plugs P5 and P6 may For telepl'icne communications, the operation* ofthe circui'tof'Fig; 4 is identical with that of Fiat fijne @sii'isignannig'equipments .entirely 'different however, f and duetto this vin difference, a transformer 100 is employed to couple the output circuit of device 13 to the input circuit of device 18.

The modulator-demodulator MD of Fig. 4 is very similar to the modulator-demodulatoreamplifier MDAiof Fig. 1, except that it does not function at any time solely as an amplifier. The amplifier A of Fig. 4L is much like the amplifier-detector AD, when the latter is functioning solely as an amplie lier.

F or call signaling, switch 101 is provided. lVhen vthis switch is thrown to its left hand position, relay 11 is energized independently of control switch CS over a circuit which may be traced from the ground side of battery 22 through battery 22, conductor 35, winding of relay 11 to ground at switch 101. Under these conditions, the oscillator O produces carrier waves in the same manner as they are produced for telephone transmis sion by the closure of control switch CS. These oscillations are impressed upon the modulator-demodulator MD but not upon the carrier transmission line ML by way of plugs PS, since relay 31 is deenergized. A distant stationsimilar to that of Fig. L1 may call the station of Fig. 4 by impressing carrier waves upon the carrier transmission line ML by means of control switch CS. These waves incoming at the local station by way of plugs P8 are also impressed upon the input circuit of modula'tor-demodulator MD by means of transformer 17. If the locally generated carrier waves and the incoming carrier waves differ from one another by an audible frequency, they will combine in the modulator-demodulator MD, producing an audible frequency component in the output circuit thereof. This audible frequency component will be impressed upon the receiver R by way of transformer 100, amplifier A, transformer 32 and closed back contacts of relay 31. The tone in the receiver produced thereby may be of sufficient volume to serve as a call signal and take the place of the clalling device 39 of Fig. 1.

Referring now to Fig. 7 a circuit arrangement for a midline repeater is there shown. This repeater is similar to the repeater shown in Fig. 24 of the Colpitts and Blaclrwell article supra. Filters HFl and LF1 associated with line MLl, and HF2 and LF2 associated with line ML2 serve the same purpose at the repeater as the respective filters HF and LF of Fig. 2 serve at a terminal station. They serve to separate the ordinary telephone transmissions from the carrier wave transmissions. Filters HGF1 HGF2 in one branch and filters LGrF1 and LGF2 in the other branch of the two-way repeater having repeater elements RE and RV function in well-known manner. The high group of carrier frequencies are amplilied by repeater element RE, while the lower and y .switch TS is thrown to the left.

group is amplified by repeater element RlV. The arrows show the directions of the trans missions.

Jac rs J10 to JN, inclusive, furnish a ready means of making connections with various parts of the circuit as will be explained more in detail hereinafter.

In Fig. 8 is shown a method of modifying the arrangement of Fig. 1 to increase the flexibility of that system. A reversing switch 109 is inserted between the contacts of relay 38 and battery 40. The switch arm 110 is made detachable from the rod of transfer switch TS by means of a removable pin 10S. An additional switch arm 107 is provided whereby the frequency of the oscillator O may be auton'iatically determined by t-he position of transfer switch TS. Thepposition of switch arm 107 determines which one of condensers 105 and 10()l is connected into the frequency determining circuit of oscillator O.

The relationship of the other parts of the circuit is clear from the reference characters since the same reference characters in all of the figures designate the same respective elements.

Should it be desired to connect the equipment of Fig. 8 to the equipment of Fig. 7 in such a manner that communication could be had over either of the outgoing lines MD or ML2 plugs P1 and P2 might be inserted in jacks Jlo and JM, respectively, and plugs P3 and P4 in jacks J, and (P3, respectively. Vith the plugs P1 and P2 so arranged for communication with a station at the distant endV of line ML1 and the transfer switch thrown to the left (the position shown) a carrier frequency in the lower group must be used. Therefore, condenser 105 must be of larger capacity than condenser 106 which is connected into the circuit when transfer switch TS is thrown to the right for conimunication over line ML2 by way of' plugs P3 and P4.

If it is desired to communicate over the line ML1 through repeater elements RE and RlV, plugs Pl and P2 would be inserted iu jacks J12 and JM. Instead of this combination, it may be desired to malte use of these repeaterelements when communicating over line ML2, in which case, plugs P3 and P4 would be inserted in jacks YP5 and J, re spectively.

The arrangement of Fig. 8 also provides a flexible system for ringing over lines ML1 and ML2. First assume that plugs P1 and P2 are inserted in jacks J 1 and J, respectively, and plugs P3 and P4 in jacks J 17 and J 13, respectively. -With the reversing switch 109 thrown downward the system is set to receive call signals from a terminal station which suppresses the carrier waves during the signaling interval provided the transfer Call sigrit) lio

nals may he received from a terminal which transmits the carrier waves during the sig naling interval provided the transferl switch TS is thrown to the right. Thus, the iaiigement described would function if the termina-l station at the distant end of lii ML1 were adapted to suppress the carrier wave during the call signaling` interval andy the termi-nal station at the distant end of line ML2 were adapted to transmit the carrier waves during the call signaling interval.

In order that the system may 4be used to receive call signalsV from both directions from terminal stations both of which suppress the carrier waves during the call sig# naling interval, pin S may yhe withdrawn so that the switch arm 110 may remain thrown to the left regardless of the position of transverse switch TS. Torreceive call signals from both directions from terminal stations both of which transmit the carrier waves during the signaling interval, the reversing switch 109 may he thrown upward.

Other possiblev combinations of r4these switches for diiferent call signaling condi, tions are shown in the following table:

Condition of catriierfwavel P051. C I I sta 10D o1 a Condition ol' Position switch arm of switch DE `arm T5 Switch Line ML 1 Line ML 2 109 Supprcssed. `Suppressed.4 Unconnected. Leit. Down. Siippessed. Suppressed. I Unconnected. Right. Up; Transmitted, Transmitted. Unconnected. Left. Up.` Transmitted. Transmitted. Unconnccted. Right: y Down. Spprcssed. Transmitted. Connected. Leitrignt. Down.

Transmitted. Suppressed. Connected. Left-right. Up.

The repeater elements RE and RW are pref-L erably electron discharge amplifying elements such as are described in connection with Figs. 2l and 22 of the Colpitts and Blackwell article supra.

Other methods of operating these circuits will no doubt he apparent to those skilled in the art and any such use in combinations, y

as defined by the appended. claims, is to he understood to come within the scope of this invention.

What is claimed is:

l. A carrier telephone terminal appara-y tus comprising an electron discharge device adapted to produce oscillations, a second electron discharge device adapted to receive modulated carrier oscillations and to translate said oscillations into signals, a microphone, and switching means for causing the iirst device to produce oscillations and to' .second and third devices with each otli-er l and with said telephone transmitter to'tfraiisinit either call or telephone signals, and still other means toassociate said second and' third devices and said telephone receiver to receive telephone signals. f

l3. A ycarrier telephone terminal; equipment comprising a first electroiidischarge device for )reducing oscillations, a second electron discharge device adapted to function as a modulator, a detector, oran amplifier, a

'third electron discharge deviceadapted to functioneither as an amplifier-or detector, a carrier wave conductor, means toassociate sai d second and third devices with said car! i rier wave conductor for the reception of call signals, means to associate said li'rst, second and third devices with said carrier wave conductors for the transmission of either rcall or telephone signals, and other ineansto associate said second andthird devicesfor the reception of telephone signals.

1l. In a carrier current terminal equip.

nient', a normallyinact'ive oscillator, al device normally functioning as a; deinouulator, a second device normally functioning" as an amplifier, telephone handset comprising a telephone transmitter, a` telephone lreceiver and apush button switclnand vmeans under` the control of saidswitch for'causing said oscillator to generate oscillations and to cause saidmodulator Vto function as an amplifier to transmit the generated oscillations tosaid second device.

5. Ina carrier wave signaling system, a carrier terminal equipment, carrier current conductors, a telephone transmitter, a te1ephone receiver, an electron discharge oscillator, an electron discharge modulator-demodulator, an electrondischarge aniplilier, a relay adapted when energized Ato close the output circuit of said oscillator and to connect said oscillator' to said modulator-demod ulator and when deenergized to open the outputciicuit of said oscillator and to connect a short-circuit in place of the oscillator output connection to said modulator-deniedgized to connect said transmitter to the input circuit of said modulator-demodulator and when deenergized to connect said carrier current conductorsto said input circuit, a

thirdrelay adapted when energized to con-Y nect said carrier `current conductors to the output circuit of said ampliiie'r and when Aulatoi, a second relay adapted when enerdecnergized to connect said receiver to said output circuit, and means to cause the energization. and deenergization oil said relays.

(3. ln'a carrier current telephone equipment, larrier current conductors, a plurality oit electron discharge devices and associated circuits adapted for transmitting and receiving signals by means ot' carrier currents, a plurality ot relays adapted when energized to connect sai-d devices and circuit to said carrier current conductors for transmitting telephone signals over said conductors and when deenergized to connect said devices and circuits to said ,carrier current conductors for receiving telephone signals therefrom, and switching nieans :tor causing the energizaton and deenergization of said relays.

7. In a carrier current terminal equipment, a normally inactive oscillator, a device normally functioning as a demodulator, a telephone hand set comprising a telephone trans niitter, a telephone receiver and a push button switch, means under the control oft said switch ior causing said oscillator to generate oscillationsand to cause said demodulator to lfunction as a modulator, and means independent oit said switch to cause said oscillator to generate oscillations andto transmit said generated oscillations to said modulator.

8. ln a signaling system, a transmission circuit for transn'iitting and receiving, a source or' waves to be transmitted, a receiving` circuit, a space discharge device having a cathode, an anode and a grid or control element, switching means for connecting` said space discharge device between said source and said transmission circuit so as to amplify the waves from said source andv impress them upon said circuit for transmission, and circuits controlled by said switching means detector.

9. In a carrier telephone terminal system comprising` a transmitting circuit, a receiving circuit, and a plurality ot space discharge devices, means for connecting said devices :in operative relationship with said transmitting circuit, and means `lor disconnecting,r said devices from said transmitting circuit and causing them to cooperate with said receiving circuit.

i0. A farrier telephone terminal. apparates con'iprising a source olf carrier waves, a source of low frequency signal waves, a space discharge modulator 'tor modulatingr f-:aid carrier waves in accordance with said low frequency waves, a space discharge ampliticr, a. transmitting circuit, and means for connecting said modulator and ampliier in said circuit, a receiving circuit, and means tor disconnecting said modulator and amplilier from said transmitting circuit and connecting them in said receiving circuit in such manner that they are caused to operate as an ampliiier and detector, respectively, of received waves.

ln .witness whereof, I hereunto subscribe my name this 4th day of January, A. D., BLS.

JOSEPH W. HoRToN. 

